(1) Field of the Invention
The present invention is a mounting bolt and sacrificial anode assembly that provides cathodic protection for fuel tanks that may be backfilled with seawater during operational purposes. (2) Description of the Prior Art
Fuel tanks have a history of corroding rapidly and requiring repairs that are costly and frequent. A major cause of leaks in fuel tanks is corrosion.
One material used for fuel tanks is aluminum alloy. Aluminum alloy (AA7175) has a favorable strength-to-weight ratio but there may be issues with corrosion resistance in the presence of seawater. Alternatively, aluminum alloy (AA6061) has enhanced corrosion resistance although with an occasional unacceptable compromise in weight.
Cathodic protection anodes are the most effective when the chemical composition and galvanic potential of the mounting hardware material is as proximate as possible to the cathodically protected material. For fuel tanks, AA 7075 mounting bolts which are identical in galvanic potential are proximate to the AA 7175 tank. Mounting bolts are easily made of AA 7075 bar stock; whereas, the tanks are made of AA 7175 used for extrusion and forging.
Additionally, welding a zinc anode to 7000 series aluminum is difficult. Furthermore, the heat from the weld changes the temper of the aluminum; thereby altering the corrosion resistance and mechanical properties of the anode and mounting bolt assembly.
Machining threads into the zinc anode is very difficult if not impossible to achieve. While the anodes could be cast with the threads in place; this would result in excessive cost in smaller quantity applications due to the need of a custom mold. Even then, the problem of subpar electrical contact would still persist.
As such, there is a continuing need for material options for use with a fuel tank in which the options provide a favorable combination of corrosion resistance and mechanical properties. This need can be addressed by the use of cathodic protection anodes which can be minimized in size to be cost-effective but with a maximized contact area that effectively maximizes needed electrical conductivity.